At the 2014 inquest into Mr McGrath's death, the coroner said if Barnard had been arrested on the robbery charge then he would have "likely been detained" and would "not have been at liberty to kill his grandfather".

A police spokesman said the force "should also have ensured the family fully understood what was happening and the process behind it".

"We have already apologised to the family, in person, and we apologise again today."